Can someone please offer some advice on baking cake layers that have straight vertical sides?  Mine are shrinking at the top, which cause them to take on the shape of a donut...  I use an oven thermometer (my oven is a little hotter than the display reads) and lowered my temp.  It caused me to have to bake longer, which was okay, but I ended up with the same shrunken top rim.  

I also use bake-even strips, which help reduce doming but don't do anything to prevent the rounded sides.  

I've tried to just deal with it and fill the side gaps in with icing but that always backfires when the icing gets the slightest bit warm and the excess weight causes it to droop.  

I use Wilton professional pans that are straight sided.  They do not nest.  I've read just as many posts claiming that straight-sided pans yield straight sides as I have read ones that claim slant-sided pans are necessary to give cakes the shrinkage room that results in straight-sided cakes. 

As you can imagine, I'm at my wits' end...  Any advice? 

I don't think I am understanding your question..  If your cake are filled correctly they should rise to the top of the pan or if you add parchment paper to the sides you can over fill slightly.  I can't visualize the sides taking shape of a doughnut .

As far as filling them...are you using a still crusting BC as a dam?  If not you should.  When you crumb the cakes start between the layers with stiff BC and push between the layers then crumb.  That should fix that issue

To me the strips may be doing you no good, adjust your heat down 25 degrees or even 50 that will/should cut the domes.  I still kind of think you do not have your pans/tins full enough.

Hope this helps

Seems to me this is a duplicate post - I think this was already addressed but in the case I'm worng here's what I suggest:

It sounds like your recipe has too much liquid.  Check into the recipe 1st.   Then don't be afraid to bake at lower temps for longer....it usually will result ina nice moist, flat cake - w/o that usual hump in the middle.  I baked almost all of my cakes at 300 degrees for about 20-40 minutes (depending on the size) , then raised the heat to 325 for an equal amount of time.  I seldom used strips or a heat core in my baking - even for the 16" cakes I made often :) 

I have had the same problem with doing cupcakes. I know the cake mixes keep getting smaller but I have added extra flour and sugar to make up the difference ( cake mix doctor suggestion).  I always bake at 325 but it seem when I take the cupcakes  out. of the oven they look beautiful  but then when the cool they shrink down to like 3/4 of the size.  What the heck is going on .....